American journalist Jill Carroll will be killed unless the United States frees all female prisoners in Iraq, according to a videotape aired on Arab television Tuesday.

The satellite network Al-Jazeera aired a silent 20-second-long videotape Tuesday night of Carroll, a freelance reporter with The Christian Science Monitor. In the tape, Carroll is shown sitting in front of a white background and speaking, but her voice is inaudible. Carroll looks pale and appears tired in the tape, and her long straight brown hair is parted in the middle and pulled back from her face.

In an accompanying message, the terrorists behind the tape threatened to kill the 28-year-old in 72 hours lest the United States give in to its demands.

The State Department said U.S. officials were doing everything possible to win Carroll's freedom.

"We continue to make every effort we can, working with Iraqis and others, to see Miss Carroll is returned safe and sound," spokesman Sean McCormack said.

Al-Jazeera would not tell The Associated Press how it received the tape but issued its own statement calling for Carroll's release. An Al-Jazeera producer said no specific group's name was attached to the message and that it was sent to the station with the tape on Tuesday.

However, a still photograph of Carroll from the videotape that later appeared on the Al-Jazeera Web site carried a logo in the bottom right corner that read "The Revenge Brigade." The group was not known from previous claims of responsibility of violence in Iraq.

The Christian Science Monitor released a statement from her family pleading with her captors to set her free.

"Jill is an innocent journalist and we respectfully ask that you please show her mercy and allow her to return home to her mother, sister and family," the statement said. "Jill is a friend and sister to many Iraqis and has been dedicated to bringing the truth of the Iraq war to the world. We appeal for the speedy and safe return of our beloved daughter and sister."

Carroll has not been heard from since she was grabbed Jan. 7 in one of Baghdad's most dangerous neighborhoods. Gunmen ambushed her car and killed her translator shortly after she left the offices of a Sunni Arab politician.

The Boston-based Christian Science Monitor said Saturday that it continued "to pursue every possible avenue" to win her release.

The U.S. military raided a prominent Sunni mosque a day after Carroll was kidnapped, sparking a demonstration by hundreds of worshippers. A U.S. military official said the raid was a necessary immediate response to the kidnapping based on a tip provided by an Iraqi citizen.

Carroll, who speaks some Arabic and wore a head covering while moving around Iraq, has been described by her editor as an aggressive reporter but not a reckless one.

Despite her language skills, Carroll used an Iraqi translator. The translator was slain by the kidnappers. The driver of their car escaped and is now safe with his family, David Clark Scott, the Monitor's international news editor, said.

Police Maj. Falah Mohamadawi said the translator told officers just before he died that the abduction took place when he and Carroll were heading to meet a Sunni Arab political leader in the predominantly Sunni Adel neighborhood.

Some American Muslim groups denounced the kidnapping of a journalist and appealed for her release.

"Journalists must be free to report on conflicts worldwide without fear of being targeted by combatants. We call for the immediate and unconditional release of Jill Carroll and for the release of all hostages held in Iraq. No cause can be served by harming those who only seek to convey the human suffering caused by war," reads a statement from the Council on American-Islamic Relations.

Insurgents in Iraq have kidnapped more than 240 foreigners and killed at least 39 of them. Some killings have been videotaped and have been tied to demands.

Last June, for example, South Korean citizen Kim Sun-il, 33, was beheaded by terrorists despite promises of an extended deadline for Korea to call off its planned deployment of about 3,000 troops to Iraq. One of the masked armed men in the video read a statement addressed to the Korean people: "This is what your hands have committed. Your army has not come here for the sake of Iraqis, but for cursed America."

Kim's body was later found west of Baghdad by American soldiers.

On Dec. 8, the Islamic Army of Iraq claimed to have killed American electrician Ronald Schulz. Other groups are holding four Christian humanitarian workers — two Canadians, a Briton and an American.

No news has emerged about the fate of those men since a group claiming responsibility for their capture imposed a Dec. 10 deadline for their killings.

Briton Norman Kember, 74, Canadians James Loney, 41, and Harmeet Singh Sooden, 32, and American Tom Fox, 54, were abducted in Baghdad on Nov. 26. All four were working in Iraq with Christian Peacemaker Teams, a Canadian-based organization that has investigated allegations of abuse against Iraqi prisoners.

The previously unknown Swords of Righteousness Brigade had threatened to kill the group if the United States and Britain did not release all detainees in Iraq.

Carroll's abduction occurred as Sunni Arab politicians are discussing their possible participation in a coalition government, which the United States hopes will help defuse the Sunni-led insurgency and heal sectarian rifts between Sunnis and Shiites.

Iraqi President Jalal Talabani predicted Tuesday that the country's most prominent Sunni Arab political group would join a national unity government once Dec. 15 election results are announced. No date has been set for the results' release.

Also Tuesday, a court official said a Shiite lawyer is expected to take charge of Saddam Hussein's trial in the 1982 massacre of more than 140 Shiites, replacing the Kurdish chief judge who resigned amid claims of government interference in the high profile case.

Said al-Hamash, the second-ranking member of the five-judge tribunal trying the former Iraqi leader and seven co-defendants, is expected to replace chief judge Rizgar Mohammed Amin, said Raid Juhi, the top investigating judge who prepared the case against Saddam.

Amin's expected resignation followed complaints over the slow progress of the trial into allegations of Saddam's involvement in the 1982 Dujail killings north of Baghdad following an assassination attempt against him.

The switch is not expected to prevent the trial's Jan. 24 scheduled resumption. The trial recessed Dec. 22 after two days of testimony. Conviction could bring a sentence of death by hanging.

Amin would be the second judge to step down. Another panel member removed himself in late November because one of the co-defendants may have been involved in the execution of his brother.

Since the trial opened Oct. 19, two defense lawyers also have been assassinated and a third has fled the country. Police also uncovered a plot to fire rockets at the courtroom in late November.

Talabani would not object to moving the tribunal from Baghdad to southern Iraq or his northern Kurdish region if the judges sought such a change on security grounds, presidential secretary Hewah Othman told The Associated Press. But any transfer is dependent on parliamentary approval.

Elsewhere, gunmen firing from cars terrorized the western Baghdad neighborhood of al-Baiyaa on Tuesday, slaying a police lieutenant driving to work before three more men — including an auto mechanic and his son — were gunned down in the same area.

Earlier in the day, the bullet-riddled bodies of an army battalion commander and his brother were also found in al-Baiyaa. Col. Hussein Shiaa and his brother were abducted Sunday after leaving their base in Mahmoudiya, about 20 miles south of Baghdad.

Police found four bound and blindfolded bodies each shot in the back of the head and dumped in a Baghdad sewer, police said. It was unclear exactly when the four were killed.

The Associated Press contributed to this report.